
Make sure SFX, Music, and Dialogue settings are set to maximum. After this, restart the game and see if it helps.
The sound mixer on your PC shows all the sources and applications from which the sound is currently coming. Sometimes we mistakenly mute the sound coming from GTA online. With the volume mixer panel, you can fix the volume for the particular game or app.
Right-click on the sound icon present at the bottom right of your taskbar and click on the Open Volume Mixer option.

Find GTA Online check the volume level settings. If it is mute, kindly unmute it.
Check Voice Chat Settings
Sometimes the settings for voice chat are preferred in a way that the game SFX sounds stop when the opponent is speaking. And if the opponent’s mic is on and he/she is not speaking, then the sound from the game will be muted.

Since voice chat cuts out all other ingame sounds, we recommend you max out “SFX” and “Music” options to the maximum.
Turn off Mute Audio On Focus Loss
Focus Loss mode was originally made to allow players to focus on their tasks better when they minimize the app. But sometimes, when you un-minimize the game tab, sounds still do not work. So you need to disable this mode all together to fix the sound issues from GTA online.
Open the GTA Settings panel and navigate to the Audio tab.

Here make sure Mute Audio On Focus Loss option is turned off. After this, restart the game and see if it helps.
Reset GTA Sound settings
If the above two methods did not help you much, then you have to reset the sound settings. It is possible that the current sound settings you have are creating a technical glitch, so resetting the sound will help. If you cannot find the reset sound settings option, you can simply re-install the game.
Open the GTA Settings panel and navigate to the Audio tab.

Here scroll down and click on the Restore Defaults option.
Consider re-installing the game the final way of fixing any sound-related issues with the game. Please note that GTA Online is a server-based online multi-player game. So once you re-install the game and log in with your account, all game progress will be back.
Conclusion
This is how you can easily tackle the situation when you are facing GTA Online Sound Not Working or Audio Cutting out/glitch. These issues are majority caused by the sound setting inside the game. If the above methods do not help you with the issue, you can re-install the game which will reset any sound settings to normal.